1. Field of the Invention
The present invention relates to a phase control device for a phased array antenna and its system, and more particularly to a phase control device for an optical control phased array antenna suitable for feeding power to a large plane expanded active phased array antenna that is mounted on a satellite or the like, and an optical control phased array antenna system.
2. Description of the Related Art
There is a rapidly expanding demand for the information communications, and the satellite communications will be increasingly more important in the future. To cope with the smaller ground stations and the large-capacity communications at high speed and in wide band, a satellite antenna tends to be larger size, and the use of a large-size plane expanding active phased array antenna as suitable for that purpose is considered.
The features of such a phased array antenna may include the flexible beam control by a phase shifter, the scanning ability of beam over wide angles, the mirror precision easily retained by the phase shifter for larger aperture and higher frequencies, and the enhanced efficiency with the trouble proof capability and reduced output of individual amplifiers, because of the high output amplifiers that can be distributed in the active array system.
A problem associated with the large-size plane expanding active phased array antenna is that it is very heavy because the feeding system consists of a waveguide or a coaxial cable. To solve this problem, an optical feeding system is conceived, whereby the feeding system is constituted of an optical component/optical fiber, making it possible to realize the small size and light weight.
A technique associated with it was proposed in an optical link for radio signal transmission to transmit a lightwave modulated with a radio signal between a radio collection and delivery station and a radio base station having a phased array antenna, in which the phased array antenna at the radio base station is enabled through the signal processing of lightwave itself (Japanese Patent Laid-Open No. 9-215048, xe2x80x9cOptical Link for Radio Signal Transmissionxe2x80x9d).
In this optical link for radio signal transmission, an optical signal having a plurality of wavelengths is modulated with a radio signal from the radio collection and delivery station to the radio base station, and a modulated lightwave with the plurality of wavelengths is subjected to a delay processing of lightwave itself for the excitation distribution control of antenna elements. The optical signal under the excitation distribution control is converted into an electrical signal, which is then distributed to each radiator. For reception, the lightwave is modulated with the radio signal received at the radio base station, and transmitted to the radio collection and delivery station for making the signal processing as lightwave itself to extract an excitation distribution given to an incidence unit.
In the conventional optical control phased array antenna (e.g., Japanese Patent Laid-Open No. 9-215048), a number of optical control phase shifting circuits represented by an optical delay path were required corresponding to the number of radiant elements to provide an excitation distribution for each radiant element of the array antenna.
Therefore, in the case where a large scale phased array antenna of hundreds to tens of thousands of elements are constituted, the size or weight of a group of phase shifting circuits corresponding to the number of radiant elements has less negligible effect on the entire system. Particularly, in the optical control phased array antenna mounted on the satellites demanding for the small size, light weight and high reliability, the weight or volume has a significant effect on the ability of satellite. Also, because a number of highly reliable components are required, the cost is increased.
Further, in the conventional technique, it was difficult to constitute a control circuit that can withstand the severe environments of the satellite antenna that is exposed to the outer space, because optical signal processing means (e.g., a phase control circuit) resides directly under the antenna.
The present invention has been achieved in the light of the above-mentioned problems, and it is an object of the present invention to provide a phase control device for an optical control phased array antenna and an optical control phased array antenna system employing the phase control device, in which the number of circuits for phase control is reduced to make the phase control circuit smaller, lighter and simpler in the entire antenna system, even when a large scale phased array antenna is made up.
The phase control device to control the optical control phased array antenna according to the present invention is employed to control the optical control phased array antenna. The phase control device includes a wavelength splitter to split an input optical signal having wavelengths corresponding to at least the number of control units of the antenna elements to be controlled for each wavelength, a plurality of phase shifters with different amounts of phase shift to change the phase of the optical signal in accordance with an excitation distribution of antenna elements, an optical switch matrix to assign a required amount of phase shift in accordance with each wavelength to lead an output at each wavelength from the wavelength splitter to one of the plurality of phase shifters, and an optical multiplexer to multiplex the outputs from the plurality of phase shifters to output a multiplexed optical signal.
Also, an optical control phased array antenna system according to the present invention has an antenna in which n2 (n2xe2x89xa61) subarray units consisting of n1 (n1xe2x89xa72) control units of antenna elements are arranged. The optical control phased array antenna system includes, one or a plurality of light sources to output a lightwave having at least nl kinds of wavelengths multiplexed, m2 (m2xe2x89xa7m1) optical modulators to modulate the lightwave having the n1 kinds of wavelengths with m1 (m1xe2x89xa71) kinds of transmitting signal, m2 splitters to split an output light from the m2 optical modulators into n2, m2xc3x97n2 phase control devices to control the optical control phased array antenna to input the outputs from the m2 splitters, m2xc3x97n2 optical transmission lines to transmit an optical signal with n1 kinds of wavelengths multiplexed that are output from the m2xc3x97n2 phase control devices to control the optical control phased array antenna, m2xc3x97n2 band splitters to split an optical signal supplied via the m2xc3x97n2 optical transmission lines into n1 kinds for each wavelength, and n1xc3x97n2 optical multiplexers to multiplex m2 kinds of optical signals having different wavelengths corresponding to the outputs from the m2 optical modulators among the optical signals output from the m2xc3x97n2 band splitters to supply a multiplexed optical signal to each of the n1 control units in the n2 subarray units.
In this present invention, for an N-bit phase shifter with 2N kinds of optical delay line optical path, for example, the optical switch matrix is employed to switch the optical path for each wavelength to assign the amount of phase shift. Accordingly, each optical delay line can be commonly utilized at different wavelengths. Therefore, the phase shifters in the phase control circuit can be reduced in number by the multiplicity of wavelengths as compared with the conventional technique.